If the upstream fails a checksum, retry from the MIRROR before giving up. If this occurs report a warning about the upstream failed checksum. This will add more robust fetching if an upstream serves a bad file or webpage. fetching of distcc prior to the move from samba -> googlecode is a good example of this.
http://git.pokylinux.org/cgit/cgit.cgi/poky/commit/?id=bf8735f83b3ad2e7366205cfb00625c335a4f910